(1) Field of the Invention
This invention relates to apparatus for drafting and parallelizing fibers for no-twist or ordinary (twisted) textile yarn.
(2) Description of the Prior Art
It is well known to those familiar with textile processing that the need to straighten and parallelize staple fibers is a most difficult and essential step in the yarn-forming process. Furthermore, it is well known that drafting or drawing is the most common method for obtaining this parallelization. Conventionally, parallelization is accomplished by a plurality of pairs of drawing rolls in series between which the fibers pass with progressively increasing speeds of rotation for the successive pairs of rolls. Each pair of rolls has a relatively firm grip on the fibers and in order to accomplish the draft, it is necessary for the several pairs of rolls to be spaced apart a distance at least slightly greater than the length of the longest fibers. This results in an uneven drawing because the fibers are always drawn at the weakest point, and in spite of careful attention to operation, uneven places in the yarn can be detected. These uneven places are commonly referred to as drafting waves. In practice various methods are used to reduce or control drafting waves, the most common of which is the use of aprons to control the fibers in the main drafting zone. Doubling or simultaneously drafting a plurality of slivers and combining them into a single sliver thus averaging the thick and thin places is another method for reducing the effect of drafting waves.
In addition to the costs associated with these efforts to produce a uniform sliver, the discontinuity caused by the need for doubling makes the yarn-forming process extremely difficult to completely automate.
Fiber drafting and parallelization is particularly important in the production of no-twist (twistless) yarn. Generally, such yarn is made by drafting and parallelizing strands of fiber, applying a temporary adhesive (liquid binder) to the fibers, drying the binder and winding the thus-produced yarn. Thereafter, the yarn is formed into a fabric by, for example, weaving, afterwhich the binder is water-washed from the fiber. Problems associated with twistless yarn are discussed in (1) "Textile Topics", a bulletin published by the Textile Research Center of Lubbock, Tex., Vol. III, No. 1, September 1979; and (2) "Twistless Yarn--A New Method For The Manufacture Of Modern Textile Fabrics" by T. H. M. Terwee, appearing in Chemielfasern/Textilindustre, Vol 29/81 (1979), E108-E110. To date, a continuous process for the production of the twistless yarn directly from card web has not been developed.